There are a type of medicaments that can be stored for a long time and that are filled in containers as e.g. cartridges, syringes, ampoules, canisters or the like, containing a ready-to-use medicament in liquid state. However, there are also other type of medicaments that are a mixture of two substances, a medicament agent (e.g. lyophilized, powdered or concentrated liquid) and a diluent (e.g. water, dextrox solution or saline solution), wherein these type of medicaments can not be pre-mixed and stored for a long time because the medicament agent is unstable and can be degraded and loses its effect quickly. Hence, a user, e.g. a patient himself/herself, a physician, a nurse, hospital personnel or trained persons, has/have to perform the mixing within a limited time period prior to the delivery of a dose of medicament to a patient. Further, some medicament agents are subject to meet significant chemical changes while mixing. Such sensitive medicament agents require a particular treatment so that, when mixing said medicament agents with a diluent, unreasonable mixing force will degrade said medicament agents.
In order to facilitate the mixing, a number of containers for mixing have been developed comprising at least two chambers, known as multi-chamber containers. These multi-chambered containers comprise a first chamber containing the medicament agent and at least a second chamber containing the diluent. These chambers are sealed off with stoppers in order that the medicament agents do not become degraded. When the medicament agent is to be mixed shortly before administering, redirecting passages are opened between the chambers, usually by depressing a distal stopper and in turn a divider stopper of the container somewhat. The passages allow the mixing of the medicament agent and the diluent and the medicament is ready for delivery.
The above mentioned requirements can be achieved by simple medicament delivery devices, such as a common hypodermic syringe, but the procedure is of course rather awkward, in particular for users not used to handle these devices. In order to facilitate for the patient themselves to administer the medicament with a predetermined dose in an easy, safe and reliable way and also to facilitate the administration of medicaments for hospital personnel in the same facilitated way, a number of automatic and semi-automatic devices have been developed in combination with these multiple-chamber solutions for obtaining a mixing before delivery.
A self-injection device arranged with a dual-chamber container, wherein both the mixing and the injection are done automatically by mechanical means, as springs and other means, is disclosed in U.S. Pat. No. 4,755,169. A similar solution is disclosed in U.S. Pat. No. 6,793,646 wherein the mixing of a dual-chamber cartridge is done is done automatically by springs upon activation of the device and the injection is done by manually applying a force to a plunger rod forwardly. A drawback with these devices is that the mixing force, to which medicament agents are subject to, is too high at the beginning due to Hookes law. Hence, the medicament agents can be degraded.
Another solution is disclosed in WO 2004004809, wherein both the mixing and the injection are done automatically by electronics controlled means. A drawback with this device is that the electronics are dependent on batteries and is very sensitive to noise, moisture, water, etc.; which can result in malfunctions. Even more the manufacture of these devices is more expensive than the manufacture of mechanical devices.
In U.S. Pat. No. 6,319,225 the mixing of a dual-chamber ampoule is done manually. The device is set to be vertical on a flat plane and then a downward press on its proximal case causes a relative upward movement of its plunger rod pressing a stopper of the ampoule with eye observation on actions inside the ampoule, such that a mixing is obtained. Though in U.S. Pat. No. 6,319,225 is disclosed that the best suitable process for mixing a medicament agent with a diluent, is by performing manual control of the diluent flow with adequate slowness which will be monitored by eye observation; a drawback with this device is that the mixing force, to which medicament agents are subject to, can be high if the user is stressed and wants to use the device as soon as possible. Hence, the medicament agents can be degraded.
Moreover, the handling and safety aspects of injector devices, having a certain degree of automatic functions, as well as immediate accessibility in emergency situations are issues that attract a lot of attention when developing this type of devices.
One important safety aspect when handling an auto-injector which is used to achieve a manual mixing and an automatic injection, is the locking of the injection means, e.g. a compressed spring actuating on a plunger rod, before the manual mixing have been completely.
One such a device is disclosed in U.S. Pat. No. 6,893,420 wherein a self-injection device is arranged with a dual-chamber body. The mixing is done manually by a screw-tightening operation and the device comprises locking means for locking a latch means that prevent the automatic penetration and injection means from being released before the mixing has been completely finished. However, this solution is rather bulky and relies also on many components acting in co-operation and in sequence, one triggering another, which may lead to a mal-function, mal-dose accuracy, or that the device becomes complicated, hence not user friendly. This device suffers from the drawback that locking means has to be actively removed from the device after the mixing has been finished. This is a step which is not intuitive for a user, who will try to push the locking means instead of removing them. Another drawback is the dose accuracy, since the penetration starts pushing the stoppers, the medicament will start to be expelled during the whole penetration sequence, leading to so called wet injections and delivering of medicament through the whole penetration tissue instead of injecting the required dose at the intended penetration depth.
Another such a device is disclosed in WO2007/115424A1 which relates to an injection device having a container holder having a multi-chamber container within, which is manually movable relative to the injection device for the purpose of mixing the components within the multi-chamber container. The device further comprises a spring which can bear on a part of the injection device, and a coupling element for coupling the container holder to the spring such that, during the movement of the container holder into the injection device, the spring is tensioned. The device also comprises an activation knob and a push button, wherein the activation knob has to be rotated for forcing the push button to protrude from the housing and thereby setting the device in a ready for injection delivery state. However, this solution suffers from the drawback that the activation knob has to be actively manipulated for releasing the push button after the mixing has been finished. This is a step which is not intuitive for a user, who will try to find where the push button or activation means are located instead of rotating the knob.
Even though the devices according to U.S. Pat. No. 6,893,420 and WO2007/115424A have proved to function well and displays a degree of safety, there is always a desire for improvements of such devices, among them being the design of the mechanism in order to simplify the manufacture and assembly in order to reduce costs but at the same time maintain or even improve the reliability of the safety and function of the device.